APPLICATION OF THE DEPTH OF CLOSURE CONCEPT

Robert J. Nicholls, William A. Birkemeier, Robert J. Hallermeier

Abstract

Using data from Duck NC (a wave-dominated, microtidal, sandy oceanic beach), depth of closure is critically evaluated. A meaningful closure is observed for most erosional events, and annual to 30 month time intervals, supporting the application of this concept within coastal engineering. However, the magnitude of depth of closure is sensitive to the definition and analysis approach utilized and estimates of closure need to be explicitly linked to this information. The limit depth d{ (Hallermeier, 1981) is found to define a conservative bound to the observations of closure during erosional events and in those annual cases where we have data. This confirms the ability to compute a meaningful limit depth simply using extreme wave conditions. At longer time scales there is evidence of a decoupling of the relationship between d{ and observed depth of closure, the observations increase less rapidly than the predictions of d{. Understanding how closure evolves from individual erosional events to annual and longer time intervals improves the interpretation of sparse surveys and can assist engineering judgement when applying closure predictions.